It is known that modern internal combustion engine can be equipped with one or more devices whose operation need a pneumatic actuation, for instance a Variable Geometry Turbocharger (VGT), a Variable Flow Turbocharger (VFT) or a waste gate valve associated to a Fixed Geometry Turbocharger (FGT). In fact, the VGT and the VFT are turbochargers designed for regulating the direction of the exhaust flow driving the turbine wheel, in order to optimize the turbine efficiency under different engine operating conditions, principally under different values of the engine speed.
For operating such regulation, a VFT generally comprises a movable flap member, whose position is adjustable to vary the geometry of the turbine chamber, while a VGT comprise a plurality of vanes inside the turbine chamber, which are arranged for guiding the incoming exhaust flow towards the turbine wheel, and which are movable so as to vary their angle. The waste gate valve is a bypass valve installed in the exhaust pipe upstream of the turbine inlet of a FGT, which comprises a movable valve element, whose position is adjustable such that, at high engine speeds, part of the incoming exhaust gas flow bypasses the turbine wheel. The movable flap of the VFT, the movable vanes of the VGT and the movable valve element of the waste gate valve are conventionally moved by a pneumatic actuator.
This pneumatic actuator can be controlled by a three-way electromechanical proportional valve (EPV), typically a solenoid valve, having a first port in communication with the atmosphere, a second port in communication with a vacuum tank or vacuum pump, and a third port in communication with the pneumatic actuator. The EPV, controlled by an engine control unit (ECU), regulates the pressure delivered to the pneumatic actuator, in a range between the atmospheric value and the negative value of the vacuum tank or pump, so that the variation of this pressure causes the pneumatic actuator to move the movable flap of the VFT, the movable vanes of the VGT or the movable valve element of the waste gate valve.
The EPV is generally manufactured as an independent device comprising an its own external casing, typically made of plastic, which is provided with the above named three ports and which encloses also a movable valve member for choking these ports as well as the solenoid for actuating this movable valve member, so that the EPV needs of being fastened to the engine or anyway to another component inside the engine compartment of the motor vehicle. However, the EPV is very sensitive to vibrations, such as those generated by the engine operation, which can cause the movable valve member of the EPV to move even if no electrical command has been issued by the ECU, thereby improperly varying the inclination of the turbine vanes. For this reason, the external casing of the EPV is usually fastened to the engine with the interposition of a plurality of supporting dampers, which are suitable for attenuating the vibrations transmitted to the EPV. By way of example, these supporting dampers can be cylindrical hollow pads made of rubber, which are individually fixed and compressed by a screw-bolt between the external casing of the EPV and a dedicated mounting bracket that is screwed on the engine.
In view of the above, it follows that the fastening of the EPV involves many individual components, which slow down and complicate the whole operation, which occupy a comparatively wide space within the engine compartment, and which are usually provided by different suppliers, thereby increasing also the quality control effort and the overall manufacturing cost. Another drawback of the above-mentioned solution for fastening the EPV is that, resting the head of the screw-bolts on the EPV casing, the tightening torque of the screw-bolts should be kept under the breaking limit of the casing material, which could be insufficient for guaranteeing a proper strength of the fastening.
Therefore, at least one aim of an embodiment is therefore to simplify and speed up the assemblage of the EPV. At least another aim is to increase the fastening strength of the EPV on the engine, without compromising a proper compression of the supporting dampers. At least yet, another aim is to reach the above-mentioned goals with a simple, rational, and rather inexpensive solution. In addition, other aimsm objects, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.